code: def test_multiprocess_data_loader(options):
      reader = MockDatasetReader()
      data_path = "this doesn't matter"
  
      loader = MultiProcessDataLoader(
          reader=reader, data_path=data_path, **options
      )
      if not options.get("max_instances_in_memory"):
          # Instances should be loaded immediately if max_instances_in_memory is None.
          assert loader._instances
  
      instances: Iterable[Instance] = loader.iter_instances()
      # This should be a generator.
      assert not isinstance(instances, (list, tuple))
      instances = list(instances)
      assert len(instances) == MockDatasetReader.NUM_INSTANCES
  
      # Now build vocab.
      vocab = Vocabulary.from_instances(instances)
  
      # Before indexing the loader, trying to iterate through batches will raise an error.
      with pytest.raises(
          ValueError,
          match="Did you forget to call DataLoader.index_with",
      ):
          list(loader)
  
      loader.index_with(vocab)
  
      # Run through a couple epochs to make sure we collect all of the instances.
      for epoch in range(2):
          indices: List[int] = []
          for batch in loader:
              for index in batch["index"]:
                  indices.append(index)  # type: ignore
          # Ensure no duplicates.
          assert len(indices) == len(set(indices)), indices
          # Ensure all collected.
          assert len(indices) == MockDatasetReader.NUM_INSTANCES, epoch
  
imports: from typing import List, Iterable, Dict
  import torch
  import pytest
  from allennlp.common.testing import requires_gpu
  from allennlp.data.instance import Instance
  from allennlp.data.dataset_readers import DatasetReader
  from allennlp.data.data_loaders import MultiProcessDataLoader, WorkerError
  from allennlp.data.fields import Field, TextField, MetadataField, TensorField
  from allennlp.data.tokenizers import PretrainedTransformerTokenizer
  from allennlp.data.token_indexers import PretrainedTransformerIndexer
  from allennlp.data.vocabulary import Vocabulary
  from allennlp.data.data_loaders.data_collator import LanguageModelingDataCollator
label_desc: Use image node_id 2 for calling a global function with example usage: test_multiprocess_data_loader(options) without return types